Considering the debates regarding lower increase in the economic growth after Brexit, the main objective of this paper is to measure the positive impact of economic integration of Central and Eastern European (CEE) countries on the UK economy and the effect of Brexit on the immigration from these countries to the UK. The European Union membership of some CEE countries increased, in average, the number of the UK immigrants by 12 times in the period 2004-2014 compared to the group of countries formed by Russia and Ukraine. The empirical findings show positive economic effects of immigration on the UK's economy, even if the pro Brexit group claimed that a control of immigration is necessary. CEE countries emigrants stimulated the UK economic growth, price stability and reduced the homicide rate. The effects of immigration on the unemployment rate, health and education spending were positive, but very low. According to mixed-effects Poisson models estimations, after Brexit the number of the UK immigrants from the CEE countries that are member of the EU might decrease by 2 times. This significant decline in immigration might impose austerity measures, because of the fall in the economic growth trend with negative impact on the UK economy. Therefore, we recommend policies that focus more on high-skilled labour force than on the reduction of the number of immigrants. The UK should propose measures to slow the expected immigration decline in order to alleviate economic issues like decline in economic growth, decrease in labour productivity, cutting backs on public services.